This invention relates to a transfer switch of the type that is adapted to be interconnected with an auxiliary power source such as an electrical generator, for controlling the supply of electrical power from the generator to branch electrical circuits in an electrical load center.
Transfer switches for use with an auxiliary power source, such as an electrical generator, are known in the prior art. A transfer switch typically performs the function of controlling the supply of power from the generator to one or more branch electrical circuits contained within a building, in the event of an outage or disruption of power from a primary power source such as a utility. Typically, the transfer switch is interconnected with selected branch circuits to supply power to electrical loads contained within the building, which normally are devices or appliances such as a furnace, sump pump, refrigerator or freezer.
The majority of prior art transfer switches are manually operated. With transfer switches of this type, the operator initiates operation of the generator and connects the generator to the transfer switch, unless there is a permanent connection between the generator and the transfer switch. The individual switches or circuit breakers of the transfer switch are then actuated to supply power from the generator to the circuits in which the individual transfer switches are connected. While this type of transfer switch arrangement functions satisfactorily, it requires the presence of a person, such as the homeowner, to undertake the operations necessary to start the generator and actuate the switches to supply power from the generator to the electrical circuits. For this reason, automatic transfer switches have been developed to automatically initiate operation of a generator upon a discontinuation or disruption in the supply of utility power, and to connect certain of the electrical circuits to the generator. Examples of such switches are illustrated in Schell et al U.S. Pat. No. 4,398,097; DeVisser et al U.S. Pat. No. 3,778,633; and Schnackenberg et al U.S. Pat. No. 6,172,432. The '432 patent illustrates a complicated switch mechanism incorporating numerous circuits and control logic for carrying out the functions of an automatic transfer switch.
It is an object of the present invention to provide a transfer switch arrangement for interconnecting branch circuits with an auxiliary power source, such as a generator, in the event of a disruption or discontinuation in the supply of power from a primary power source, such as a utility. It is a further object of the invention to provide such a transfer switch arrangement in which power is supplied to the branch circuits in accordance with a predetermined order of priority, while providing a protection feature that prevents an overload condition on the generator. It is a further object of the invention to provide such a transfer switch arrangement which enables certain of the branch circuits to be connected automatically and others of the branch circuits to be connected manually, or which enables all of the branch circuits to be connected manually to allow the user to override the automatic actuation sequence when desired. Yet another object of the invention is to provide such a transfer switch arrangement which is relatively simple in its components and construction, to provide a relatively low cost of manufacture, while nonetheless providing safe and reliable interconnection of branch circuits with the generator.
In accordance with the present invention, a transfer switch arrangement is adapted to be interposed between an auxiliary power source, such as a generator, and an electrical load center which is interconnected with a primary power source, such as utility power. The electrical load center includes a series of branch electrical circuits, each of which is connected with an electrical load. The transfer switch arrangement includes a series of switches, each of which is interconnected between the auxiliary power source and one of the branch circuits. The switches are normally in a first contact position in which the branch circuit is supplied with power from the primary power source. Upon actuation, each switch is movable to a second contact position in which the branch circuit is connected to the auxiliary power source. In one form, the switches are transfer-type switches and certain of the switches, are solenoid-driven for movement between the first and second contact position.
The transfer switch arrangement includes a controller interconnected with the series of switches. When electrical power from the primary power source is initially discontinued, the controller is operably configured to sequentially actuate the solenoid-driven switches for movement from the first contact position to the second contact position to sequentially connect the branch circuits to the auxiliary power source, preferably in accordance with a predetermined order of priority. During sequential actuation of the switches, the controller is operably configured to return any one of the solenoid-driven switches to the first contact position in the event actuation of the switch to the second contact position results in the total load on the auxiliary power source exceeding a predetermined threshold, to discontinue the supply of electrical power to the individual branch circuit from the auxiliary power source. The controller is further operably configured to monitor the load on the generator, and to re-actuate the switch when the load on the generator falls below the total load that existed prior to the previous attempt to actuate the switches. The controller continues to thereafter sequentially continue movement of the switches from the first contact position to the second contact position, in accordance with the predetermined order or priority, until all of the solenoid-driven switches are moved from the first contact position to the second contact position. The controller is further operably configured to continue to monitor the total load on the generator after all of the switches have been moved to the second contact position, and to return all of the switches to the first contact position from the second contact position in the event the total load on the generator exceeds the predetermined threshold. Thereafter, the controller is operably configured to again sequentially move the switches from the first contact position to the second contact position, again in accordance with the predetermined order of priority, to restore the supply of power from the auxiliary power source to the branch circuits.
The transfer switch arrangement includes a utility voltage sensor which is connected to the controller and to at least one of the branch circuits. The utility voltage sensor provides an input signal to the controller during operation of the utility power source. The controller reads and evaluates the input signal and determines whether the supply of utility power has been discontinued, according to predetermined parameters. If so, the controller actuates a generator starting circuit to initiate operation of the generator. A current sensor detects the load on the generator, and is interconnected with the controller which ascertains the current load on the generator and de-actuates the actuated switch, or all of the actuated switches, to the second contact position in the event the current load on the generator exceeds the predetermined threshold. A generator voltage sensor is connected to the controller and to the output of the generator, for providing an input signal to the controller during operation of the generator. The controller reads and evaluates the input signal and determines whether the supply of generator power is acceptable, according to predetermined parameters.
The controller functions to actuate certain of the switches according to the predetermined order of priority, to supply certain of the electrical loads with auxiliary power from the generator. The transfer switch arrangement may also include one or more additional switches interconnected with additional electrical loads, which can be manually actuated by the user to supply power to additional loads in the event the user is present during the utility power outage.
The invention contemplates a transfer switch arrangement as described above, as well as a method of supplying electrical power to a series of electrical loads upon a disruption in a primary source of electrical power, substantially in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.